Conventionally, motor field coils are manufactured using the progressive winding technique illustrated in FIGS. 1a-1c hereof. A complete coil turn is placed in each slot along the axis of the coil form, see FIG. 1a. After the first layer of turns is completed, the turns are advanced radially outward to begin a second substantially concentric layer, as illustrated in FIG. 1b. In so doing, the first turn of the second layer must cross over the last turn of the first layer at an angle. Such a crossing is referred to herein as a normal crossover. In like manner, a second normal crossover occurs after the second layer is completed, and the next turn is advanced radially outward to begin the third layer, as illustrated in FIG. 1c. Thus, there is one normal crossover for each new layer of coil turns.
A problem which occurs in any multi-concentric layer coil is that the normal crossovers create a bulge in the coil profile. This is particularly problematical with the progressive winding technique described above because all of the normal crossovers occur on one side (the lead-end side) of the coil. This creates a build-up or bulge in the coil profile which significantly limits the number of turns that can be wound within the permissible coil envelope.
To overcome the build-up problem referred to above, it is known to employ a retrogressive winding technique in which one-half turn in every other layer of the coil is omitted. This results in normal crossovers which occur on alternate sides of the coil, thereby distributing the build-up between the lead-end side of the coil and the opposite side of the coil. This permits more turns to be wound within the permissible coil envelope but still leaves unoccupied spaces in the coil where the half turns were omitted. In other words, the retrogressive method improves the copper utilization of the coil but falls short of maximizing the copper utilization.